RESEARCH PROGRAM: The overall goal of this clinical center is to increase scientific understanding about the nature of SLI through broad and intensive study of children identified as language impaired (LI). The most unique aspect of this program is that it will utilize a very large and representative epidemiological sample of language impaired children. A minimum of 185 children with SLI (e.g., language impairments but normal nonverbal IQs) will be compared with 185 language-impaired youngsters of borderline IQ (under 85) (NLI), with 400 normally developing children (N), and with 80 normal language children with low nonverbal IQs (low cognitive (LC)) from kindergarten through fourth grade. The six subprojects that comprise this clinical center address a variety of interrelated issues. Subproject 1 will examine two contrasting approaches to the diagnosis of SLI (psychometric and morphosyntactic) and will investigate the relations among various modes of diagnosis of SLI and outcome. In Subproject 2, two parameters of processing speed (reaction time and presentation rate) will be examined in the SLI, NLI, and normal control groups to investigate the hypothesis that processing speed deficits underlie SLI. Subproject 3 will investigate reading and writing outcomes of SLI and NLI children, as well as of the children in the N and LC groups. Subproject 4 will examine the relations among speech problems, language disorders, and psychosocial impairment. Various hypothesized subtypes of developmental phonological disorder will be investigated and the relations among these subtypes and various genetic markers will be examined. Subproject 5 will monitor all interventions received by the subject population, examine the relations between LI and psychosocial impairment, and analyze subject characteristics, intervention factors, and language environment factors as determinants of outcome of SLI using path analytic models. Finally, Subproject 6 will examine the molecular genetics of language and phonological impairment by utilizing the phenotypic characterization provided in the other subprojects and then looking for genetic mechanisms.